Due to their high applicability to various products and electrical properties such as a high energy density, secondary batteries are not only commonly applied to portable devices, but universally applied to electric vehicle (EV) or hybrid electric vehicle (HEV) that drive on an electric driving source. Secondary batteries are gaining attention for their primary advantage of remarkably reducing the use of fossil fuels and not generating by-products from the use of energy, making them a new eco-friendly and energy efficient source of energy.
Currently, commonly used secondary batteries include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, and nickel zinc batteries. These unit secondary battery cells, i.e., unit battery cells have the working voltage of about 2.5V˜4.2V. Thus, in case that higher output voltage is required, a plurality of battery cells may be connected in series to form a battery pack. A battery pack may be also formed by connecting a plurality of battery cells in parallel based on the charge/discharge capacity required for the battery pack. Accordingly, the number of battery cells in the battery pack may be variously set based on the output voltage or charge/discharge capacity required.
Meanwhile, in case that a battery pack is formed by connecting a plurality of battery cells in series/in parallel, it is general to form a battery module using a plurality of battery cells first, and then form a battery pack using a plurality of battery modules with an addition of other elements.
Here, a conventional battery module has at least one cell cartridge in which at least one battery cell is mounted to guide the stacking of the battery cells and prevent the battery cells from moving. Generally, a plurality of cell cartridges stacked on top of each other guides the stacking of the plurality of battery cells. The conventional battery module designed to constrain the battery cell using the cell cartridge generally constrains the battery cell from moving by applying the pressure in the surface direction of the battery cell, to prevent the battery cell placed in fixed position from moving due to vibration or impacts. Furthermore, a foam pad is inserted between the battery cell and the cell cartridge to mitigate the volume expansion of the battery cell caused by electrode expansion and gas generation.
FIG. 1 is a schematic top view of a cell cartridge connected with battery cells according to the related art, and FIG. 2 is a cross-sectional view taken along the line II-II′ in FIG. 1.
Referring to FIGS. 1 and 2, the cell cartridge 2 is formed by injection molding to fix the edges of the battery cell body, and when two battery cells 1 are mounted in the cell cartridge 2, the edges that constitute the periphery are inserted into the cell cartridge 2 and the battery cells 1 are received in the cell cartridge 2. In the conventional battery module, when the edges of the battery cells 1 are inserted into the cell cartridge 2, impacts or vibration occurring during mounting may be transmitted to the edges of the battery cells 1, causing damage to the battery cells 1, for example, breakage of an electrode assembly or an electrode lead 3 within the battery cells 1.
Describing in further detail with reference to FIG. 3 which is a partial enlarged diagram of section III in FIG. 2, movements in the x direction may be constrained by the contact of the shoulder of the battery cell 1 indicated by “a” and the cell cartridge 2, but if the pressing continues, the thickness of a separator in the battery cell 1 may be reduced, or the edge of an electrode may be broken, causing a short.
Furthermore, as shown in the section indicated by “b”, the electrode lead 3 of the two battery cells 1 are fixed by welding, but the body of the battery cell 1 may move in the x direction due to vibration and impacts, causing damage to the lead 3 of the battery cell 1.
In addition, seeing the section indicated by “c”, the edge of the battery cell 1 touches a counterpart such as the cell cartridge 2. Accordingly, in case that cell swelling occurs during charging/discharging of the battery cell 1 and BOL→EOL, it is difficult to create an internal gas pocket area, and the ultrasonic welded part in the battery cell 1 may be damaged, increasing the risk of a short. In case that the structure of the cell cartridge 2 is changed to prevent the edge of the battery cell 1 from touching the counterpart such as the cell cartridge 2, it is difficult to form a structure for fixing the battery cells 1 in the lengthwise direction.
As described above, because the conventional battery module structure has many problems, a new module structure is needed. Because the size and weight of the battery module are directly related to a receiving space and output of a corresponding medium and large device, manufacturers make efforts to fabricate battery modules having smaller size and lighter weight while ensuring higher output. To this end, it is necessary to develop a module structure that is simple, compact and sure to fix battery cells without using the conventional cell cartridge, so that the entire battery pack does not have a complex structure and does not occupy a large space.
Meanwhile, a new module structure should involve a change of a foam pad. This is because the conventional module structure is difficult to uniformize the applied pressure to control the cell pressing and swelling through a foam pad due to the tolerance of each element in the mass production.